God Mode
Once in the game, press F1. This will bring up the Diary screen. Type in the cheat you want to activate it:

liveforever - God mode
canttouchthis - Can't be knocked down or knocked back

Typing in the cheat again from the Diary screen will turn that cheat off.

Instantly Win or Lose Level
Once in the game, press F1. This will bring up the Diary screen. Type in the cheat you want to activate it:

winlevel - Instantly Win Level
loselevel - Instantly Lose Level

Typing in the cheat again from the Diary screen will turn that cheat off.

Regenerate
Once in the game, press F1. This will bring up the Diary screen. Type in the cheat you want to activate it:

elderrune - Regenerate health over time

Typing in the cheat again from the Diary screen will turn that cheat off.

Show Frame Rate
Press [Crtl]-[Shift]-[Y] to display your frame rate on the screen.

Slow Motion and Cloak
Once in the game, press F1. This will bring up the Diary screen. Type in the cheat you want to activate it:

carousel - Slow Motion Mode
moonshadow - Phase Cloak

Typing in the cheat again from the Diary screen will turn that cheat off.